Karel Jelínek Department of Electronics and Vacuum Physics

1. Charles University, Prague Faculty of Mathematics and PhysicsPosition and velocity of Earth’s bow shock Karel Jelínek Department of Electronics and Vacuum Physics Supervisor: Prof. RNDr. Zdeněk Němeček, DrSc.

2. Content • motivation • solar wind • experimental setup • data source • current model of bow shock • aim of work • statistical results • future plan

3. Motivation Collisionless bow shock attracts attention of many plasma physicist. Its ability of heating more ions then electrons can be helpful for thermonuclear fusion. The bow shock also accelerates particles on its front and therefore, it is a source of high energy particles. Such shocks often occur in space if a supersonic plasma flows onto obstacles like comets, planets and also galaxy. The Earth's bow shock provides necessary dissipation of kinetic energy of the solar wind (this occurs at a very short length). Many works deal with a study of shape and position of the bow shock but a systematic analysis of the bow shock velocity is still missing.

4. Solar wind averaged parameters of the solar wind in 1 AU distance from the Sun.

5. magnetopause interplanetary magnetic field bow shock magnetosheath Magnetosphere of the Earth solar wind

6. Classification of bow shock classification of BS accordingBn definition of the angleBn paralel quasiper- pendicular pendicular quasiparalel bow shock parallel BS perpendicular BS BS BS magnetopause BS BS

7. Current Earth’s bow shock models (disadvantage) • set of crossings when the bow shock is in motion (majority of these crossings are due to changes of solar wind parameters and BS changes its position from one to other stationary state, therefore, we observe BS during its motion and the observed position of BS does not correspond to solar wind conditions) • fitting of quadratic surface (paraboloid, ellipsoid, ...) • only dynamic pressure and Mach number are driving parameters of fitted surface (magnetic field plays a small role in models) • a shape of the magnetopause does not involve the cusp

8. Aim of work • identification of exact time when BS crosses through both of spacecraftsInterball-IaMagion-4 . • estimation of the BS velocity (vBS) from timing and location of observed BS. • determination of solar wind parameters for estimated vBS from satellite WIND(e.g.n,B,vBS,T )and computation of Bn,MAlfvén and, which are the main parameters controlling processes on BS. • find out some dependencies between the BS velocity and solar wind parameters.

9. BS crossing locations Data source BS crossings were observed by Interball-1 Magion-4 spacecrafts For monitoring of the solar wind, we have used the WIND satellite. 190 of events were observed by both spacecrafts 114 of events were identify only by one spacecraft

10. 16. FEB 1996 23:00:07 – 00:00:12 BSM4 BSM4 electron energy spectra ion energy spectra direction toward the Sun ion energy spectra tailward direction Faraday’s cups Determination of the time of BS crossings electron energy spectra ion energy spectra tailward direction magnetometer Faraday’s cups BSM4 BSIB

11. 16. FEB 1996 23:00:07 – 00:00:12 BSM4 BSM4 electron energy spectra ion energy spectra direction toward the Sun ion energy spectra tailward direction Faraday’s cups electron energy spectra ion energy spectra tailward direction magnetometer Faraday’s cups BSM4 BSIB

12. BS velocity computation

13. Resulting histogram of BS speeds events Resulting histogram of BS speeds. The velocities range from 0 – 100 km/s but a majority of them (70%) is less than ~ 40 km/s – this is in agreement with previous studies.

14. dependence of the BS velocity on its location Statistical results one spacecraft both spacecrafts X direction distance to X axis

15. dependence of the BS velocity on the solar wind velocity and on change of velocity Statistical results one spacecraft both spacecrafts velocity change of velocity

16. dependence of the BS velocity on particle density and on change of particle density Statistical results one spacecraft both spacecrafts density changes of density

17. dependence of the BS velocity on change of IMF and on angle Bn Statistical results one spacecraft both spacecrafts change of IMF Bn

18. number of events vsh [km/s] The histogram of shock velocities for quasiparallel and quasiperpendicular shocks.

19. Conclusion • The bow shock is in a permanent small-scale motion. • The bow shock velocities are usually smaller than but velocities exceeding can be observed (these results are consistent with previous findings, e.g., Lepidi et al.,1996). • We identify about 830 of the BS crossing. • 114 of this events were observed only by one spacecraft. • From 190 of the BS crossings which were observed by both spacecrafts we computed average velocity of the BS motion. We analyze how the BS velocity depends on the solar wind parameters, we find out: • bigger velocity of SW=> bigger velocity of the BS • bigger change of SW velocity => bigger velocity of the BS • bigger density of SW => smaller velocity of the BS • bigger change of IMF => bigger velocity of the BS • qvasiparallel BS is faster then quasiperpendicular • other parameters of SW have not significant effect on BS velocity

20. Future plan • look for more BS crossings • starts case study with interesting events • employ statistical study of the BS velocity to improve model of BS location

21. Positions of INTERBALL-1 and MAGION-4 spacecrafts during observations of BS crossings for 27 FEB 1997.

22. Thank you for your attention